Re: Trying to decode a TLS 1.3 with null cipher

[Ahmed Elsherbiny <sherboah () gmail com>]

Hello Peter,

First of all, thank you again for creating the patch. I did test it and was
able to successfully decode some messages.
My implementation uses WolfSSL v4.3.0.

I hope the patch will be merged in, please let me know if there's any more
info you need from my end.

Regards,
Ahmed


On Sat, May 2, 2020 at 3:21 PM Peter Wu <peter () lekensteyn nl> wrote:

> Hi Ahmed,
>
> I have posted a patch at https://code.wireshark.org/review/37034 which
> should allow you to see the plaintext. However there is a big open
> question about the draft specification. Can you share some more details
> on your implementation, in particular which TLS library do you use?
>
> Without more answers, this patch will not be merged.
>
> Kind regards,
> Peter
>
> On Sat, May 02, 2020 at 10:55:07AM -0700, Ahmed Elsherbiny wrote:
> > Wow this is great news, thank you Peter!
> >
> > Regards,
> > Ahmed
> >
> > On Sat, May 2, 2020 at 10:21 AM Peter Wu <peter () lekensteyn nl> wrote:
> >
> > > Hi Ahmed,
> > >
> > > On Fri, May 01, 2020 at 02:10:01PM -0700, Ahmed Elsherbiny wrote:
> > > > Hello,
> > > >
> > > > I've written a dissector for a custom protocol. The dissector works
> well,
> > > > and now I'm trying to run the protocol over TLS 1.3.
> > > >
> > > > The cipher suite being used is TLS_SHA256_SHA256 (Code: 0xC0B4).
> This is
> > > a
> > > > new cipher suite, it is used for integrity and has a null cipher (The
> > > > payload is actually plaintext). It is still in draft form, here is
> the
> > > > document that describes it:
> https://www.ietf.org/id/draft-camwinget-tls-ts13-macciphersuites-05.txt
> > > > Looking at the ServerHello packet, Wireshark shows the CipherSuite as
> > > > Unknown (0xC0B4). Consequently, it does not provide a "Decrypted
> > > > application data" tab and does not pass the data to my dissector.
> > >
> > > The new cipher name was added in the development build via commit
> > > v3.3.0rc0-513-g3e2a837cc0 (https://code.wireshark.org/review/36052).
> It
> > > is not present in the stable build yet.
> > >
> > > > This is what the TLS debug log shows:
> > > [..]
> > > > I tried adding the cipher-suite to packet-tls-utils.c and recompiling
> > > > Wireshark. This is the line that I added, since the document says
> that
> > > > Diffie-Helman is the only key exchange that can be used. I'm not
> > > completely
> > > > sure that I'm using the correct macros - I don't fully understand
> TLS.
> > > > {0xC0B4, KEX_DH_ANON, ENC_NULL, DIG_SHA256, MODE_GCM }
> > >
> > > This is not correct, TLS 1.3 has a different key exchange (KEX_TLS13)
> > > and more changes are needed to ensure that existing TLS 1.3 ciphers do
> > > not break while adding support for this new cipher.
> > >
> > > I've created a test samples for the two ciphers and posted these at
> > > https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=16543
> > >
> > > I hope to have a patch available tomorrow.
> > > --
> > > Kind regards,
> > > Peter Wu
> > > https://lekensteyn.nl
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